1. Field of the Invention
This invention relates to sample/hold amplifiers which track an input signal during sample mode, and retain the last value of the input signal when switched to hold mode. More particularly, this invention relates to sample/hold amplifiers having auto-zero compensation to substantially reduce errors in the level of the signal retained in the hold mode.
2. Description of the Prior Art
Sample/hold amplifiers have been used for many years and particularly with data acquisition systems, e.g. to maintain constant the input signal to an A/D converter during the conversion interval. Many types of sample/hold amplifiers have been proposed, with special attention being directed to techniques for avoiding errors such as due to offset voltages in the amplifier circuitry. One recent example of such prior art is U.S. Pat. No. 4,587,443 wherein a pair of amplifiers are arranged in cascade, with the interconnection between the amplifiers being switched in a criss-cross fashion when transferring from sample to hold.
In general, prior art sample/hold apparatus has suffered from important deficiencies, including excessive errors for use with high-performance systems, and/or undue complexity with resultant high cost of manufacture. The present invention is directed to providing an improved sample/hold amplifier which has excellent performance capabilities together with circuit simplicity.